Reflective Particle Tag (RPT) technology is in use for physical authentication of a tagged item. Generally, conventional RPT technology entails a field-applied tag, such as a bar code, and a seal composed of a random distribution of specular mineral particles, such as hematite, embedded in an adhesive. When illuminated from different angles, a RPT presents complex patterns of millimeter-scale light reflections unique to the tag. Generally, an RPT procedure entails measuring reference reflected light patterns upon field application of the seal which are recorded in association with the tag (e.g., bar code) to a reference database. Subsequent authentication then entails remeasuring the light reflecting patterns of the seal and comparing the patterns to those recorded for the tag in the reference database. A mismatch is indicative of seal tampering, for example where a seal is broken to access an item's contents or to relocate the tag to another item.
Advances in imaging and computing technology have permitted automation of the RPT procedure, enable greater inspection efficiency and wider adoption by various regulatory authorities. Techniques to increase the uniqueness of an RPT, for identifying the source of a RPT for example, and/or to provide additional protection against sophisticated methods of tampering, such as bisection and delamination, are therefore advantageous.